1. Field of the Invention
The present invention relates to a light guide panel for uniformly emanating light introduced from a side end surface uniformly from a front surface, and a plane illuminator apparatus using the light guide panel, which illumination apparatus is suitable as a backlight source for a large-sized transmission type liquid crystal display.
2. Description of the Prior art
A plane illuminator apparatus for use in a backlight source for a transmission type liquid crystal display includes a light source such as a cathode-ray fluorescent luminescence tube (CFL), an LED array and the like, and a transparent light guide panel. Light emanated from the light source is guided from one end side of the light guide panel. The light incident in the light guide panel emanates finally uniformly from a front surface portion of the light guide panel or from all of a back surface portion utilizing total reflection of the light. The aforementioned plane illuminator apparatus generally has a diagonal line length of about 356 mm (14 inches) or less corresponding to the size of the transmission liquid crystal display.
Since in the prior art light guide panel and the plane illuminator apparatus light introduced from a one end side of the light guide panel thereinto, the amount of light emanated from the front surface portion of the light guide panel or the back surface portion has a tendency of attenuating as the light goes away from the one end side. For the purpose of emanating light uniformly from the entire region of the front surface portion of the light guide panel, there is formed a light deflection portion possessing finer unevenness for deflecting light propagating in the light guide panel to the outside of the light guide panel on the front surface portion of the light guide panel and/or on the back surface portion of the same. The rate of the distribution of the light deflection portion is set such that it is increased as it goes away from the one end of the light guide panel, through which the light emanated from the light source is introduced.
FIGS. 6 and 7 illustrate a relationship between a position of the one end side of the light guide panel from a light incident end surface and an area of the light deflection portion occupying per unit area, i.e., an occupation rate. FIG. 7 illustrates a situation where owing to reflected light from the other end surface of the light guide panel located in opposition to the incident end surface the amount of the light emanated from the neighborhood of the other end surface is likely to be increased, so that more uniform light emission is ensured than that illustrated in FIG. 6 by decreasing an occupation rate of the light deflection portion in the vicinity of the other end surface.
In recent years, in a large-sized transmission liquid crystal display having a diagonal line length exceeding 381 mm (15 inches) which can be manufactured, there are disposed a set of light sources on opposite ends of the light guide panel in opposition to each other such that a uniform distribution light amount emanates from a front surface portion of the display and simultaneously an enough illumination light amount is ensured. Herein, the distribution of the light deflection portion formed on the light guide panel is fundamentally designed such that the distribution of the light deflection portion illustrated in FIGS. 6 and 7 is symmetrical on the opposite sides of the light guide panel, more specifically there is increased the occupation rate of the light deflection as it lies more closely to the one set of the light sources with respect to the center of the light guide panel.
In such a light guide panel, the amount of the light emanated from the neighborhoods of the opposite end sides of the light guide panel is not only relatively increased but also the distribution of the amount of the light emanated from the entire region of the front surface portion of the light guide panel becomes uneven. Particularly, in a light guide panel set such that an occupation rate of the light deflection portion is more increased as it goes toward the one set of the light source side with respect to the center, the amount of the light emanated from the front surface portion of the light guide panel in the vicinity of the opposite end sides is sharply increased. As a result, it is unlikely to uniformize brightness distribution of the liquid crystal display. Moreover, visibility is deteriorated owing to uneven brightness.
Although in the light guide panel where the occupation rate is reduced of the light deflection portion located on the opposite sides of the light guide panel and in close vicinity of the one set of the light source based upon the distribution state of FIG. 7, such inconvenience is reduced, it fails to ensure a substantially uniform brightness distribution of the liquid crystal display and hence it is difficult to ensure excellent visibility.
It is accordingly an object of the present invention to provide, in a plane illuminator apparatus in which at least one set of light sources are employed to permit light to be incident from both opposite end sides of the light guide panel, a light guide panel capable of uniformizing distribution of an emanated light amount from a front surface of the light guide panel and the plane illuminator apparatus employing the foregoing light guide panel.
In a first aspect of the present invention, a light guide panel comprises at least one set of opposing incidence end surface portions into each of which light from a light source is introduced, a front surface portion from which the light introduced from the set of the incident end surface portions is emanated, a back surface portion located on the opposite side to the front surface portion, and many light deflection portions formed on at least one between the front surface portion and the back surface portion. The rate of the light deflection portion per unit area located along the one incident end surface portion from the other incident end surface portion is set to be two Gauss distributions, and a peak of the first Gauss distribution is shifted on the side of the one incident end surface portion while a peak of the second Gauss distribution is shifted to the side of the other incident end surface portion.
In accordance with the present invention, the rate of the light deflection portion per unit area extending from a one incident end surface portion along the other incident end surface portion is set to be two Gaussian distributions, and a peak of the first Gaussian distribution is displaced on the side of the one incident end surface portion while a peak of the second Gaussian distribution is biased on the side of the other incident end surface portion, so that substantially no light deflection portion is existent in the vicinity of each incident end surface portion. The amount of the emanated light from the front surface portion of the light guide panel substantially depends upon a distance from the incident end surface portion and the Gaussian distributions of the light deflection portion. This enables the light to be uniformly emitted from the front surface portion of the light guide panel without being influenced by the size of the light guide panel. Further, uniform brightness distribution corresponding to the brightness of the light source is ensured.
In the light guide panel according to the first aspect of the present invention, the peak of the first Gaussian distribution may be more biased to the center of the light guide panel extending from the one incident end surface portion to the other incident end surface portion rather than the side of the one incident end surface portion while the peak of the second Gaussian distribution may be more biased to the center of the light guide panel extending from the one incident end surface portion to the other incident end surface portion rather than the side of the other incident end surface portion. Since the peaks of the two Gaussian distributions are hereby located in close vicinity of the center of the light guide panel, even if there is employed a large-sized light guide panel having a long distance from the one incident surface portion to the other incident end surface portion, the light is successfully uniformly emanated from the front surface portion. Further, there is ensured uniform brightness distribution corresponding to the brightness of the light source.
Herein, the other incident end surface portion side with the first Gaussian distribution and the one incident end surface portion side with the second Gaussian distribution are set to be prevented from being averaged, and the light deflection portion having a directivity is employed, whereby even if the size of the light guide panel is very large, the light can be uniformly emanated from the front surface portion. Additionally, there is ensured uniform brightness distribution corresponding to the brightness of the light source.
The light deflection portion is configured as an isosceles triangle when projected perpendicularly to the front surface portion, and has a pair of vertical conical surfaces rising substantially vertically from the front surface portion and an inclined conical surface inclined with respect to the front surface portion such that a bottom side is parallel to the incident end surface portion. Otherwise, the light deflection portion may be an indentation constructed as a part of a spherical surface with a predetermined radius of curvature in the back surface portion.
When the light guide panel is rectangular plate shaped, two sets of incident end surface portions opposing to each other may be provided. Herein, the two sets of the incident end surface portions intersect each other in their opposing direction to ensure bright illumination light.
In a second aspect of the present invention, a plane illuminator apparatus comprises a light guide panel including a front surface portion from which light emanates, a back surface portion located on the opposite side of the front surface portion, and at least a set of opposing incident end surface portions putting these front surface portion and back surface portion, a set of light sources for projecting toward the set of the incident end surface portions of the light guide panel respectively, and a light reflection sheet for covering portions other than the front surface portion of the light guide panel and the set of the incident end surface portions. The rate of the light deflection portions per unit area extending along the one incident end surface portion from the other incident end surface portion is set to be two Gaussian distributions, and the peak of the first Gaussian distribution is biased to the side of said one incident end surface while the peak of the second Gaussian distribution is biased to the side of the other incident end surface portion.
In the plane illuminator apparatus according to the second aspect of the present invention, the peak of the first Gaussian distribution may be more biased to the center of the light guide panel extending from the one incident end surface portion to the other incident end surface portion rather than the side of the one incident end surface portion while the peak of the second Gaussian distribution may be more biased to the center of the light guide panel extending from the one incident end surface portion to the other incident end surface portion rather than the side of the other incident end surface portion. Since the peaks of the two Gaussian distributions are hereby located in close vicinity of the center of the light guide panel, even if there is employed a large-sized light guide panel having a long distance from the one incident surface portion to the other incident end surface portion, the light is successfully uniformly emanated from the front surface portion. Further, there is ensured uniform brightness distribution corresponding to the brightness of the light source.
Herein, the other incident end surface portion side with the first Gaussian distribution and the one incident end surface portion side with the second Gaussian distribution are set to be prevented from being averaged, and the light deflection portion having a directivity is employed, whereby even if the size of the light guide panel is very large, the light can be uniformly emanated from the front surface portion. Additionally, there is ensured uniform brightness distribution corresponding to the brightness of the light source.
The light deflection portion is configured as an isosceles triangle when projected perpendicularly to the front surface portion, and has a pair of vertical conical surfaces rising substantially vertically from the front surface portion and an inclined conical surface inclined with respect to the front surface portion such that a bottom side is parallel to the incident end surface portion. Otherwise, the light deflection portion may be an indentation constructed as a part of a spherical surface with a predetermined radius of curvature in the back surface portion.
When the light guide panel is rectangular plate shaped, two sets of incident end surface portions opposing to each other may be provided. Herein, the two sets of the incident end surface portions intersect each other in their opposing direction to ensure bright illumination light.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.